Threaded fasteners including bolts, studs, nuts and washers are known and used in traditional bolting applications. Maintenance and repair of industrial applications begin with loosening of and end with tightening of these threaded fasteners. Naturally industry seeks to reduce production loss during routine, unforeseen and/or emergency maintenance and/or repair. The importance of accurately and consistently controlling tension and/or preload applied to threaded fasteners increases with precision or criticality of parameters and tolerances of the industrial application as a whole.
There are two methods of tightening and/or loosening a bolt, torque and tension. Until Applicant's innovations, however, it was not possible to perform hydraulic torqueing and hydraulic tensioning with the same tool. Operators needed separate tools to torque and tension threaded fasteners.
Torque has benefits in that it: can be applied to most existing threaded fasteners; is accurate within five percent (5%) of pre-calculated turning resistance of nut; avoids unintended loosening; assures more even circumferential bolt load than tension; and overcomes uneven lubrication applications, foreign particulate underneath the nut or on top of the flange and minor thread damage. Torque, however, has detriments in that it: is subject to thread friction and facial friction, both of which are unknown; requires use of back-up wrench applied to the nut on the other side of the application to keep still the bottom portion of the threaded fastener; results in unknown residual bolt load; and is subject to bolt torsion and side load, both of which adversely affect bolting applications. Sustainable and accurate use of torque in bolting requires establishing thread and bearing facial frictions and eliminating torsion and side load.
Tension has benefits in that it is torsion- and side load-free. Tension, however, has detriments in that it: requires the bolt to stick out by at least its diameter over and about the nut, so that it can be pulled upwards by a tensioner, which often necessitates bolt and nut replacement; is accurate only within 25% of assumed turning resistance; yields unpredictable, manual nut seating; is subject to thread friction and facial friction, both of which are unknown; often over pulls, not stretches the fastener; results in uncontrollable fastener relaxation due to load transfer from puller; and results in unknown residual bolt load. Sustainable and accurate use of tension in bolting requires eliminating stud/bolt pulling and load transfer.
Torque power tools are known in the art and include those pneumatically, electrically and hydraulically driven. Torque power tools produce a turning force to tighten and/or loosen the threaded fastener and an equal and opposite reaction force. Hydraulic tensioners use a puller to apply hydraulic pressure to the bolt, which is usually results in a 10%-20% higher than desired bolt elongation, causing the stud to be over pulled. Then the nut is hand tightened until snug; the pressure on the cylinder is released; the stud springs back; and the load is transferred from the bridge to the nut thereby compressing the joint with clamping force.
Conventionally, hydraulic torqueing of threaded fasteners for industrial applications may be controlled by monitoring operation parameters including either hydraulic or pneumatic fluid pressures or flow rates, electrical circuit parameters such as current, voltage or magnetic field, torque output values, rotation speeds, or a combination of such. Fastener load control through such monitoring may yield unpredictable and inconsistent results due to, similar inherent drawbacks as described above. Where it has been attempted to obtain greater uniformity through use of lubricants or the like, results have continued to be unsatisfactory.
Another approach has been to electronically monitor torque as a function of angle of rotation. Such arrangements still do not directly measure fastener tension, and in addition require expensive assembly and control hardware. A third approach has been to tighten the fastener while reacting off of the stud, the washer or an adjacent stationary object. A subset of this approach is tightening to a point at which the fastener material yields and a splined fastener head separates from the threaded body. Arrangements of this type suffer from similar inherent drawbacks as described above and increased cost and system complexity.
A further technique for controlling fastener preload has been found to yield particularly consistent results. This technique, termed “torque-turn” or “torque-angle,” involves initially tightening the fastener to a specified torque, and thereafter tightening the fastener through an additional pre-determined angle. The initial tightening torque is empirically predetermined to be one at which the fastener is tightened in assembly but has not yet been substantially elastically stretched. By thereafter tightening the fastener through an additional angle or fraction of a turn, advantage is taken of the precision machining of the fastener threads so as to obtain predetermined elastic stretching of the fastener within the assembly.
Particular to hydraulically operated torque and tension tools there remains a need in the art for inexpensive equipment that may be employed by operators in the field for obtaining precision control of fastener loading. Additionally, the products on the market that perform such a function are large and cumbersome. These products use torque angle detection techniques that inhibit their ability as well as for the operability in constrained spaces.
Retainers for drive shafts in hydraulic torque wrenches are well known and often include bushings or bearings using conventional spring clips, snap rings and/or separate cap assemblies. Often special tools are needed to install or remove these prior art solutions. Absent due care, components of prior art solutions are lost or damaged during tightening and/or loosening operations. Prior art solutions may include an attached chain or lanyard between the spring clip, snap ring and/or cap assembly and the drive shaft to reduce component loss and/or damage and increase safety. The chain or lanyard, however, is undesirably loose and dangles off of the tool. Operators often operate torque wrenches with improperly retained drive shafts. Components of prior art solutions not properly seated often come off creating dangerous and unsafe operating conditions.
Applicant offers viable solutions with respect to retainers of unitary construction for drive shafts in hydraulic torque wrenches per co-pending Patent Cooperation Treaty Application Serial No. PCT/US2014/050002, having Filing Date of 6 Aug. 2014, entitled “APPARATUS FOR TIGHTENING THREADED FASTENERS”, an entire copy of which is incorporated herein by reference.
No viable solutions exist for integration of torque and angle with hydraulic torque wrenches which: limit inherent drawbacks as described above; increase operator safety through unitary construction; may be used in all industrial bolting situations, whether regular or limited clearance; and decrease bolting system cost and complexity.
Accordingly, it is desirable to provide a device that is capable of determining the angle of rotation applied to a fastener as well as display the current angle of rotation.